Let's start our investigation one verse earlier in 27:38 Solomon addresses an assembly or some chiefs or commandants as the word al-mal' الملأ was also translated. And we have an idea of the constitution of this assembly: In Verse 27:17 we learn that this assembly was of human, jinn and/or birds.
Verse 27:39 shows that the first to answer was a jinn.
Of course we know that a bird can hardly bring the throne and therefore we can only assume it is a jinn or a human who would be able to do so by a God given power!
If we further assume that the jinn who answered was the strongest among the jinn, as else he wouldn't answer. So after the birds failed and the jinn failed, we can conclude that only a human who had a knowledge that nobody else had could fulfil this task. I don't want to exclude jinn as we know they knew about the thorah, especially as this knowledge is described as a widsom of scripture.
The majority of mufassireen say it was a man from the entourage of Sulayman, his scribe or a wise man some even quoted his name like here in tafsir ibn Kathir:
(One with whom was knowledge of the Scripture said: ) Ibn `Abbas said, "This was Asif, the scribe of Sulayman.'' It was also narrated by Muhammad bin Ishaq from Yazid bin Ruman that he was Asif bin Barkhiya' and he was a truthful believer who knew the Greatest Name of Allah. Qatadah said: "He was a believer among the humans, and his name was Asif.'' (qtafsir)
However abu ala al-Maududi says in his tafsir:
Nothing is known with certainty as to who this person was, what special knowledge he had and what Book is referred to here, whose knowledge he had. No explanation of these things has been given either in the Qur'an or in any authentic Hadith. Some of the commentators say that it was an angel; others say that it was a man. Then they differ as to the identity of the man. Someone mentions the name of Asaf bin Barchiah, who, according to the rabbinical traditions, was the Prince of Men. Someone says that he was Khidr; someone mentions some other name; and Imam Razi insists that it was the Prophet Solomon himself. But none of these has any reliable source for his information, and Imam Razi's opinion does not even fit in with the Qur'anic context. Likewise, about the Book also the commentators differ. Someone says that it refers to Lauh-i-Mahfuz (the Preserved Tablet) and some other takes it for the Book of Law. But all this is mere guess-work. Similar guesses have been made about the knowledge the man had from the Book. We only know and believe what has been said in the Qur'an, or what becomes evident from its words In any case the person was not from among the jinns, and possibly he was a man. He possessed some extraordinary knowledge, which had been derived from some Divine Book (al-Kitab) . The jinn had claimed to fetch the throne within a few hours by means of his physical strength; this man fetched it in a moment by the power of his knowledge.